General Science GK Questions with Answers – Page 92

Pascal's law says that pressure applied to an enclosed fluid is transmitted undiminished to every part of the fluid and to the walls of the vessel, so a modest push on the brake pedal creates a pressure in the brake fluid that is passed to the wider pistons at every…

In a capillary tube the height of rise is directly proportional to the surface tension of the liquid and inversely proportional to its density and the radius of the tube.

In such a fluid the shearing stress is directly proportional to the rate of shear, so the coefficient of viscosity, which measures the resistance to deformation, keeps the same value whatever the stress applied; water, air, petrol and thin oils behave in this way.

The upthrust on a body is the resultant of the pressure forces of the fluid around it, and that resultant acts through the centre of gravity of the fluid the body has pushed aside, which is why the point is called the centre of buoyancy.

A floating body displaces its own weight of fluid, so the fraction of its volume that lies below the surface equals the ratio of its density to the density of the fluid, here 920 divided by 1000, which is 0.92.

By Archimedes' principle the upthrust on a body equals the weight of the fluid it displaces, and that weight is the volume of the body actually immersed multiplied by the density of the fluid and by the acceleration due to gravity.

A colloid is named according to the states of its two parts, the dispersed phase and the dispersing medium, and an emulsion is defined as a colloid in which a liquid is dispersed in another liquid, so the dispersing medium must itself be a liquid.

A molecule of water contains two atoms of hydrogen and one of oxygen.

In crystallisation a hot saturated solution is allowed to cool slowly, and as it cools only the required substance comes out of solution in the regular form of crystals while the impurities, present in smaller amounts, stay dissolved in the liquid that is left behind, which is called the mother…

When salt dissolves in water it breaks up into separate ions, which are far smaller than the wavelength of visible light, so they cannot scatter a beam sideways and the path of light through the liquid stays invisible.

Chromatography separates substances that are dissolved in the same solvent and present in very small quantities, by letting the solution creep along a strip of filter paper.

Ammonium chloride passes directly from the solid to the vapour state on heating, without melting, while common salt does not.

Brass is made by melting copper with zinc, and the resulting homogeneous mixture is harder than copper, easier to cast and machine and gives the familiar yellow colour used for utensils, fittings and musical instruments.

When two miscible liquids boil at temperatures far apart, ordinary distillation is enough, because the more volatile liquid boils off almost completely before the other begins.

Kerosene and water do not mix, so on standing they form two distinct layers with the lighter kerosene above the denser water.

Milk is an emulsion in which tiny globules of fat are dispersed through water, and those globules fall within the colloidal size range, so milk looks uniform to the eye, does not separate on standing, passes through filter paper and shows the Tyndall effect.

The particles of a colloid are between one and one thousand nanometres across, which is large enough to scatter a beam of light sideways and make the path of the beam visible.

Common salt is sodium chloride, in which sodium and chlorine are chemically combined in a fixed ratio by mass, and the result has properties quite unlike either element, since sodium reacts violently with water and chlorine is a poisonous gas while their compound is eaten daily.

Thomas Graham found in 1833 that a light gas spreads through a porous partition faster than a heavy one, and that the rates of two gases are in the inverse ratio of the square roots of their densities, and therefore of their molar masses.

At ordinary atmospheric pressure carbon dioxide has no liquid stage: the solid passes straight into vapour at about minus 78.5 degrees Celsius.